The present invention relates to a method and arrangement for adapting the starting gear of a heavy vehicle having an automated manual transmission. The invention further relates to a computer program adapted to perform such a method when said program is run on a computer, and a computer program product comprising such program code means stored on a computer readable medium. The method is advantageous for vehicles travelling in long queues or heavy traffic with several stops and starts.
Modern vehicles are often provided with a cruise control system in order to improve the comfort of a driver. Some cruise control system are provided with further functions, such as an adaptive control system that uses distance measuring equipment to monitor the distance to a vehicle in front of the own vehicle, in order to be able to adapt the cruise speed to the speed of the vehicle in front. Such a system will improve the safety of the cruise control system since a minimum distance or a minimum time interval will be maintained to the vehicle in front. Some systems will also brake the vehicle if the minimum distance or the minimum time interval is not maintained, or if the distance to the vehicle in front decreases at a certain rate. The cruise control system may be adapted to maintain a set speed by using only the propulsion torque from an engine, or by also using the brakes of the vehicle. This is especially common in heavy vehicles which are equipped with auxiliary brakes, such as engine brakes and retarders. A further function of the cruise control system of the vehicle may be an economy drive setting, in which the regulating parameters of the cruise control system are ruled by economy. The distance or time interval to a vehicle in front may be measured in different ways, but a radar device is often used.
Many heavy vehicles are also provided with an automated manual transmission (AMT), which is a manual transmission provided with one or two clutches which are engaged and disengaged automatically. In this way, an automated gear change is provided without the need to use a regular automatic transmission having a torque converter. By using an AMT, the weight and complexity of the transmission is reduced, and reduced fuel consumption is also possible. An adaptive cruise control may also give input to the control unit of the AMT such that the cruise control can use also the transmission to maintain the set cruise speed.
In a vehicle having an AMT, the start gear is selected automatically even though it is possible for the driver to select a specific start gear. The control system detects vehicle parameters such as load of the vehicle, type of engine, engine performance, inclination, selected driving mode, etc and pre-selects a suitable starting gear. The starting gear is normally selected as high as possible in order to improve the comfort for the driver and to reduce the number of gear changes.
There are however occasion where such a behaviour can be improved. There is thus a need for an improved method and arrangement for adapting the starting gear of a heavy vehicle.
It is desirable to provide an improved method for adapting the starting gear of an automated manual transmission in a heavy vehicle. It is also desirable to provide an improved arrangement for adapting the starting gear of an automated manual transmission in a heavy vehicle.
In a method for adapting the starting gear of an automated manual transmission in a heavy vehicle, where a pre-selected starting gear is selected by a control unit depending on vehicle parameters of the heavy vehicle, the starting gear is lowered from the pre-selected starting gear in dependency on a movement behaviour of a vehicle in front of the heavy vehicle.
With an aspect of the inventive method, the starting gear of an automated manual transmission in a heavy vehicle can be adapted to the current traffic situation. Normally, the starting gear is determined and set by a control unit of the vehicle. The starting gear is normally selected depending on different vehicle parameters, such as total weight of the vehicle, the load, the trailer configuration, engine performance etc. The starting gear is selected such that, with the given vehicle parameters, the vehicle will be able to perform a proper start cycle without too much clutch slippage.
The inventive method is, according to an aspect thereof, especially useful when the vehicle is standing in a queue. The adaptation of the starting gear is done by lowering the starting gear from a pre-selected starting gear in dependency of the movement behaviour of the vehicle in front. In this way, a starting gear can be selected such that the vehicle will reach the estimated speed of the vehicle in front with the starting gear, when the clutch is fully engaged. The starting gear is lowered by one or more gears. The advantage of lowering the starting gear is that the clutch will be fully engaged when the starting cycle is completed. By adapting the starting gear to the movement behaviour of the vehicle in front, the starting gear can be used also when the vehicle continue to travel in the queue, such that an unnecessary shift down must not be made after the start cycle, or such that unnecessary clutch slippage is avoided.
The adapted starting gear is preferably selected depending on the type of movement behaviour of the vehicle in front. If the movement behaviour of the vehicle in front is an acceleration, the rate of acceleration is used to determine if and how much the starting gear is to be lowered in order to be able to perform a proper start cycle. If the movement behaviour of the vehicle in front is a substantially constant speed, the selected starting gear is selected such that the own vehicle will reach a speed that corresponds to the vehicle in front when the start cycle is completed. On the other hand, if the movement behaviour of the vehicle in front is such that it is determined that the pre-selected starting gear is the best choice, an adaptation of the starting gear is not made. This may e.g. be the case if the vehicle in front accelerates with a relatively high rate or if the distance to the vehicle in front is relatively long.
The determination of when to adapt the starting gear by selecting a lower starting gear, and by how much the starting gear is lowered, is preferably governed by predetermined threshold values based on the movement behaviour of the vehicle in front.
In an arrangement for adapting the starting gear of an automated manual transmission in a heavy vehicle, where the arrangement comprises a control unit adapted to pre-select a starting gear depending on vehicle parameters of the heavy vehicle, the problem is solved in that the arrangement comprises means for detecting a movement behaviour of a vehicle in front of the heavy vehicle, and that the control unit is adapted to lower the starting gear from the pre-selected starting gear depending on the detected movement behaviour of the vehicle in front.
By this first embodiment of the arrangement for adapting the starting gear of an automated manual transmission in a heavy vehicle, the arrangement comprises a control unit adapted to pre-select a starting gear depending on vehicle parameters of the heavy vehicle and means for detecting movement behaviour of a vehicle in front of the heavy vehicle. The control unit is adapted to lower the starting gear from the pre-selected starting gear depending on the detected movement behaviour of the vehicle in front. The control unit may e.g. be a transmission control unit which preferably interacts with an adaptive cruise control unit, or may be integrated in the adaptive cruise control unit. The control unit may also be a stand-alone control unit or it may be integrated in any suitable control unit. The means for detecting movement behaviour of a vehicle in front is preferably a radar, even though other technical solutions such as image detection, a laser scanner or a radio transmission between the vehicle in front and the vehicle behind in order to send information about the movement behavior, are also possible solutions.